Any water they find is going to be frozen. But that doesn't mean anything alive in it before the freeze won't become active again when it thaws....
Ultra Violet exposure is likely to kill anything living it it...at least it does with any earth bred organisms. In any case it isn't likely much from space will reach Earth without having been processed and inspected (hopefully.
There is ore or minerals on Earth from which hydrogen can be extracted. Perhaps they will exist out there too. Then they need a source of oxygen and with both they can produce power with water being a byproduct.
Hopefully, they will have more secure "borders" between Earth and space than we have in this country.